Throughout this paper I shall be using the term Guided Weapon to describe a weapon which receives corrections to its direction of flight after leaving the launching device, the corrections being related in some way to the measured relative positions and behaviour of the target and weapon. With this definition some rocket weapons are guided, others are not; most of the so-called ballistic missiles are not. I must also emphasise that the opinions expressed are my own, although I gratefully acknowledge the permission of the Ministry of Defence, Navy Department, to publish the paper. I have drawn on UK Naval experience, in much of which I have been personally involved, but at various stages the evolution of Naval guided weapons has been mixed inextricably with that of the other Services’ weapons. For this reason I chose a more general title for the paper.